1. Field of the Invention
The present invention relates to rotating string trimmers of the type used by homeowners and landscapers to cut growing vegetation. More particularly, the present invention relates to trimmer heads that automatically dispense additional trimmer line as the exposed trimmer line wears away.
2. Prior Art Description
String trimmer machines have been commercially sold for many decades. In this period of time, there have been many variations to the design of the string trimmer machine and especially to the trimmer head.
The trimmer head is the part of the string trimmer machine that rotates. The trimmer head holds lengths of trimmer line that rotate with the trimmer head. The rotating trimmer line contacts and cuts vegetation as it spins.
Depending upon the make, model, and manufacturer of the string trimmer machine, the trimmer head rotates either clockwise or counterclockwise during operation. The mix in the current retail market is evenly split between clockwise and counterclockwise rotating string trimmer machines.
There are many types of trimmer heads on the market. The most common types of trimmer heads are the bump-feed trimmer head and the automatic-feed trimmer head. Both types of trimmer heads contain an internal spool that holds a reserve of wound trimmer line. As the trimmer line wears away, it can be replaced from the internal spool. In a bump-feed trimmer head, a short length of line is released from the spool when the bottom of the trimmer head is impacted or “bumped” against a hard surface. In an automatic-feed trimmer head, a short length of line is released from the spool when a predetermined change in centrifugal forces occurs that indicates that the existing trimmer line has become too short. Many mechanisms exist in the prior art for controlling the release of wound trimmer line from the internal spool of a trimmer head. Bump-activated trimmer heads are exemplified by U.S. Pat. No. 5,881,464 to Collins, entitled Line Head For Flexible Line Trimmer. Automatic-feed trimmer heads are exemplified by U.S. Pat. No. 5,060,384 to Everts, entitled Automatic Head For A Line Trimmer; and U.S. Pat. No. 5,109,607 to Everts, entitled Automatic Line Trimmer Head.
Many problems exist with traditional trimmer head designs. Primary among those problems are problems concerning the twisting of string on the spool. Most trimmer heads contain two separate lengths of trimmer line. A trimmer head relies upon centrifugal force to pull the trimmer lines from the spool. If the trimmer lines tangle, twist, or become buried under subsequent windings, the trimmer lines will not dispense in the proper manner. The trimmer head must then be disassembled, the trimmer string unwound and again rewound in the proper manner before the trimmer head will again work as designed. Furthermore, whenever the trimmer string supply is exhausted, the trimmer head must be manually disassembled. The spool is removed and rewound with a new supply of trimmer line. The spool is then reassembled back into the trimmer head. This process is difficult, labor intensive and highly time consuming. Furthermore, the entire process is often too difficult for many homeowners to complete successfully or even attempt. This is especially true with automatic feed trimmer heads that contain complex internal string release mechanisms that are contained within the trimmer head.
Another problem associated with traditional feed trimmer heads is the complexity and reliability of the release mechanism that draws trimmer line from the spool when needed. As many homeowners will attest, the mechanism for releasing the trimmer line is usually the first part of a string trimmer machine that fails to work. Once the release mechanism fails, the trimmer line must be periodically pulled out of the trimmer head using the operator's hands. This is both a time consuming and dangerous operation.
Yet another disadvantage of traditional trimmer heads is that most bump-activated trimmer heads and all known automatic-feed trimmer heads are designed to rotate in only a single direction. Accordingly, a trimmer head designed for a clockwise trimmer will not work on a counterclockwise trimmer. Furthermore, the parts from a clockwise trimmer head cannot be interchanged with any of the parts from a counterclockwise trimmer head. This requires a trimmer head manufacturer to create two sets of manufacturing tools, one for clockwise trimmer heads and one for counterclockwise trimmer heads. This significantly increases the cost associated with manufacturing trimmer heads. Furthermore, it results in each trimmer head design having two different models, one for clockwise rotation, and one for counterclockwise rotation. This significantly increases the chances that a consumer will purchase the wrong type of trimmer head for his/her string trimmer machine when looking for a replacement.
A need therefore exists for an automatic-feed string trimmer head that has an inexpensive yet reliable mechanism for dispensing trimmer line when needed. A need also exists for an automatic-feed string trimmer head that dispenses trimmer line without the trimmer line tangling, twisting, or binding. Furthermore, a need exists for an automatic-feed trimmer head that does not have to be disassembled to have new string added. Lastly, a need exists for an automatic-feed trimmer head that can be manufactured inexpensively and in a manner where many of the parts from a clockwise trimmer head are identical to parts in a counterclockwise trimmer head. These needs are met by the present invention as described and claimed below.